Development and performance of ternary binders incorporating scallop shell powder and slag for hydraulic road applications

This study investigates low-carbon ternary binders incorporating scallop shell powder (SSP) and ground granulated blast furnace slag (GGBFS) as partial substitutes for CEM II/A-LL 42.5, with replacement levels up to 90 wt.%. Increasing SSP–GGBFS substitution reduced flowability due to the finer particle size and morphology of both additions. Calorimetry and Vicat tests showed that SSP enhances early hydration and slightly reduces initial setting time up to 50% substitution, while higher levels are governed by clinker dilution and delayed slag activation. Mass loss and shrinkage over 90 days indicated that moderate substitution (30–50%) maintains dimensional stability comparable to the reference. At the hardened state, the 50% blend reached strength equivalent to CEM II/B 32.5, while very high substitutions (80–90%) still met hydraulic road binder (HRB) requirements, reaching ∼35 MPa at 90 days. Microstructural analyses confirmed portlandite consumption, C–A–S–H formation, and matrix densification. HighlightsTernary SSP–GGBFS binders were developed with up to 90% cement substitution.Early hydration enhanced by SSP and GGBFS ensures long-term strength.A 50% blend reaches CEM II/B 32.5 and 80–90% meet HRB requirements.C–A–S–H and calcite formation densify the matrix after portlandite consumption.